Sockets for electrically interconnecting a circuit board daughtercard to a circuit board mothercard are well-known. Such sockets include an insulative housing having an elongated slot for receiving an edge portion of the daughtercard. Contacts in the housing extend into the slot for engagement with contact pads on the daughtercard, and the contacts have leads which extend to an exterior of the housing for engagement with mating circuit traces on the mothercard.
The sockets may be either of the cam-in or direct insertion type. The cam-in type allows the daughtercard to be inserted into the slot at a first orientation with a zero insertion force. The card is then pivoted to a second orientation against spring forces exhibited by the contacts, and the card is retained in the second orientation by a latching device.
In the direct insertion type of socket, the daughtercard is inserted into the slot with a single straight line motion. There may be considerable resistance to insertion of the card due to friction forces of the contacts wiping against the card as the card is inserted into the slot. The contacts exert a normal force on the card in the slot, and these normal forces generate a frictional resistance to removal of the card from the socket. The frictional resistance contributes greatly to retaining the card in the socket and may be sufficient to retain the card in some cases. However, the cards are manufactured with a tolerance on their thickness, and a card that is near the minimum thickness will experience less frictional resistance than a card that is near the maximum thickness. Since vibration, shock and thermal stresses can cause a card to back out of its socket, additional retention mechanisms have been employed to ensure retention of the card therein.
U.S. Pat. No. 4,973,270 discloses a direct insertion type socket having card guides at each end which define grooves aligned with the card receiving slots. Opposed walls of each groove include a pair of opposed ridges which are spaced apart by a distance which is less than a minimum thickness of the card to be received therein. One of the walls is relatively thin so as to be somewhat flexible. Insertion of a daughtercard between the walls deflects the flexible wall and expands the groove, thereby frictionally retaining the card. The flexible wall also accommodates cards having different thicknesses.
A problem with this socket arises in that a card which is near the maximum allowable thickness is retained with a relatively high frictional force which may make extraction difficult. Further, components of modern electronic packages are mounted in close proximity, thereby limiting access to the components and hindering extraction of cards from their sockets. In order to aid card removal, sockets having a positive extraction mechanism have been developed. U.S. Pat. No. 4,990,097 discloses a card extraction member having a projection at one end which underlies the circuit card, and a handle at an opposite end. The extraction member upwardly slidable to uplift the circuit card from the socket. Pivotable extraction members are also known.
U.S. Pat. No. 5,074,800 discloses a pivotable lever having a locking mechanism and an extraction mechanism for a card edge connector. The extraction mechanism comprises an extractor foot that underlies the circuit card to enable ejection thereof. The locking mechanism includes lock arms having projections which engage in an associated locking hole in the circuit card from opposite sides thereof to lock the card in the socket. A problem exists in that circuit cards, or module cards, are produced in at least two standard types each having a locking hole at a respective specified dimension from an edge of the card. The locking projections must be disposed to engage in the locking hole of one of the standard card types, and the locking projections for different card types are not interchangeable. Also, due to dimensional tolerances on the lever and the card, there is a possibility that a load may be placed on the extractor during locking of the card in the socket. There is a need for a locking and extraction mechanism which will accommodate different standard card types. There is also a need for a locking and extraction mechanism which will eliminate the possibility of placing a load on the extractor during locking of the card in the socket.